In the field of small engine ignition systems, there are several known methods of providing spark advance. Spark advance is desirable because it may be used to provide an ignition impulse which occurs at approximately top dead center of an engine piston, to allow easy starting of the engine, as well as to provide an advanced spark to increase the power available from the engine and avoid spark knock at higher engine speeds. It also increases the efficiency of the engine at operating speed.
There are several known ways of accomplishing spark advance in large and small internal combustion engines. Historically, there are spring loaded weights which rotate a breaker-point cam or a electronic-sensor trigger wheel with respect to a driven shaft in response to engine speed changes. Step advance in electronic or magneto ignition systems has been accomplished using a rotor with various arrangements of axial or radial apertures and projections which affect a magnetic field sensed by a pickup coil in different amounts at different engine speeds, or a plurality of trigger coils of different sensitivity which are effective to cause an ignition impulse at different engine speeds. This results in the generation of two separate ignition-triggering signals, one for a retarded ignition impulse, and one for an advanced ignition impulse, both following the charging of an energy storage device, such as a coil or capacitor. Ignition advance occurs when the first signal following the charging of the energy storage device is large enough to trigger the discharge of the energy.
Thus, the prior art either requires a mechanically-complex rotor, or the use of a device, such as a trigger coil, positioned a large number of angular degrees about a flywheel away from the circuit containing the energy storage device. This results in two packages, each requiring an air gap setting to a flywheel, with interconnecting wires, or a physically large package.
The instant invention overcomes these and other complexities and disadvantages of the prior art.